1. Technical Field
The present invention relates to a display method that is suitable for utilizing for an electronic paper and the like, and to a display medium and a display device using the method thereof.
2. Related Art
Along with the advancement of computerization in recent years, the amount consumed of paper as a communication medium is continuing to increase. However, as a medium for replacing paper, electronic paper, an image display medium with which recording and deleting an image can be repeated is gathering attention to. In order to put the electronic paper to use in practice, it is required that the electronic paper, as portable, lightweight and not bulky (thin) as paper, requires little energy for rewriting, and has high reliability with little deterioration with repeated rewriting.
Display technologies that are suitable for use in such a display medium include methods in which display is carried out by depositing and dissolving metals such as silver through application of electric fields or light irradiation utilizing an electrolyte like a silver salt solution (for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2000-338528, 2005-92183, 2004-18549, 2004-198451, and the like), and methods in which display is carried out by utilizing organic photochromic materials such as fulgides (for example, JP-A Nos. 2003-131339 and 2003-170627).
However, when the purpose of utilizing electronic paper is considered, although monochrome display is basically the most important, the ability to display color is also important, because good visual quality and a wide array of representations are realizable.
As for color display, for example, in the methods described in JP-A Nos. 2000-338528 and 2005-92183, in which the combination of an electrolyte and applications an electric field is utilized, various kinds of color display can be carried out by utilizing color filters. In addition, in the methods described in JP-A Nos. 2004-18549 and 2004-198451, in which the combination of an electrolyte and light irradiation is utilized, color display can be carried out in principle by illuminating light having the same color as that to be displayed. In this method, a polychromatic photochromic material, which consists of titanium oxide bearing silver particles, is used and the color display is carried out by irradiating light with a predetermined wavelength onto this polychromatic photochromic material.
On the other hand, the methods using a photochromic material, as described in JP-A Nos. 2003-131339 and 2003-170627, can easily carry out color display by combining materials having different coloration properties.
However, when a color filter is used in the method described in JP-A Nos. 2000-338528 and 2005-92183, in which the combination of an electrolyte and electric field application is utilized, it is difficult to obtain high resolution. In addition, since the thickness of the display medium is also increased, it is also considered that the display medium becomes too bulky for use in place of paper media.
Further, in the methods described in JP-A Nos. 2004-18549 and 2004-198451, in which the combination of an electrolyte and light irradiation is utilized, specific color can be displayed. However, through diligent investigation the inventors have found that the method has difficulty in obtaining sufficient coloration density.
As mentioned above, in order to carry out color display by conventional methods using an electrolyte, it is necessary to use a color filter, and coloration density is insufficient.
On the other hand, the methods using a photochromic material as described in JP-A Nos. 2003-131339 and 2003-170627 are excellent in terms of ease in which color display can be carried out, however, the reliability of the methods is considered to be low in comparison with methods using an electrolyte for long-term use, because organic materials are used.